Cryptococcus neoformans is a significant cause of morbidity and mortality in patients with impaired T cell function, particularly those with AIDS. Presumably then, T cell responses to cryptococcal antigens are critical for protection against this ubiquitous fungus. Mannoproteins (MP) appear to be the major component recognized by the anticryptococcal cell-mediated immune (CMI) response in mice and in humans. The experiments proposed in this application are focused upon defining selected aspects of the molecular basis for CMI to C. neoformans. The driving hypothesis behind the proposed studies is that mannose receptors (MR) on dendritic cells (DC) mediate endocytosis of C. neoformans MP, resulting in efficient MHC class II-restricted antigen presentation and the initiation of a protective T cell response. There are three specific aims. Aim 1: Explore the role of dendritic cells in the immune response to C. neoformans mannoproteins. Particular attention will be paid to the role of DC mannose receptors as endocytic receptors allowing for the efficient capture of MP. Subsequent cellular events following antigen uptake will be studied including; DC maturation, antigen processing, presentation of peptide fragments, and initiation of a polarized T cell response. Aim 2: Examine the molecular determinants of the immune response to two C. neoformans mannoproteins, MP88 and MP98. Recombinant MP98 and MP88 will be generated in a prokaryotic vector, yeast vector, and mammalian cell vector. This will allow us to compare the immune response to antigens that contain the identical protein core but that qualitatively and quantitatively differ with regards to glycosylation. Aim 3: Test the capacity of mannoproteins and other C. neoformans components to protect mice from experimental cryptococcosis. The protective efficacy of immunization regimens, including ex vivo pulsed DC, will be determined and the molecular determinants of protection explored. Completion of these studies over the next five years should add significantly to our knowledge of the molecular basis for the development of a CMI response to cryptococcal antigens and could suggest novel strategies for vaccination against this often deadly mycosis.